Proportional control system



1951 E. M. WILLIAMS 2,565,540

PROPORTIONAL CONTROL SYSTEM Filed Jan. 27, 1945 FIG.I

{I4 l5 l8 FILTER I REcEIvER L I I FILTER I a 1I l l i LCONTROYL OUTPUT DEVICE I J I6 FIG.2

INVENTOR EVE RARD M. W] LLIAMS Patented Aug. 28, 1951 UNITED STATES PATENT OFFICE PROPORTIONAL CONTROL SYSTEM Everard M. Williams, State College, Pa.

Application January 27, 1945, Serial No. 574,940

2 Claims.

The invention described herein may be manufactured and. used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a radio telemetering system and more particularly to a remote control device which transmits a continuously graduated positional control.

Previously devised positional control devices have been characterized by objectionable cornplexity and their action has been uncertain or objectionably falsified by the influence of extraneous factors. A tone modulation on a radio carrier, to effect a remote control and to make the degree of control proportional to the intensity of modulation, has been used previously. This type of device has been found to be unreliable because of changes in signal loudness due to changes in distance between the signal transmitter and the signal receiver. Increasing this distance causes signal fading which makes the device unreliable.

In the present device two tones of different frequencies are used for the control signal. The signals may be graduated by causing one tone to increase in intensity, while the other tone decreases in intensity. At the receiver the effective response is made proportional to the ratio of the two tone intensities. With this provision in use, fading or interference affects both signals equally and their proportionate intensities are not affected. The system so operating pro. vides a device that is characterized by a highly reliable positional control.

The objects of the present invention comprise the provision of a device that uses the ratio of the intensities of two audio tones to effect a proportionate remote control; that uses a proportionate control which ranges from values of one sense thru a null value to values of the opposite sense; and a graduated control that is free from failure due to varying carrier strength or to interference and jamming, that is positive in action and that is simple in operation, reliable and accurate.

With the above and other objects in view which will be apparent to those who are informed in the field of remote control radio system devices from the following description, an illustrative embodiment of the present invention is shown in the accompanying drawing wherein:

Fig. 1 is a block diagram and schematic view of a ground control part of the system; and

Fig. 2 is a block diagram and schematic view of an air-borne part of the system.

lib

The present invention comprises as parts thereof a ground control station that is shown in Fig. 1 and a controlled station that is shown in Fig. 2 of the accompanying drawing. The ground control station that is shown in Fig. 1 comprises a control input device I, including a manual control 4 and 5 to which a desired control is applied, a transmitter I2, and and an antenna l3.

In the circuit that is shown in Fig. 1 of the drawing, a control that is to be transmitted is applied by hand to movable contact arms 4 and 5, that are ganged together and that engage two substantially duplicate potentiometer resistors 2 and 3. The potentiometer 2 is connected across an oscillator 6 and the potentiometer 3 is connected across an oscillator l. The magnitude of the voltage that is supplied from oscillator 6 is equal to that supplied from oscillator 'l. The voltage across the potentiometer 2 is of a frequency f2 and the voltage across the potentiometer 3 is of a frequency is that differs from the frequency is. The frequencies f2 and f3 Preferably are selected to be in non-harmonic relation with respect to each other to prevent or minimize mutual interference, and particularly to prevent cross-modulation in succeeding stages of the apparatus.

The two ganged contact arms 4 and 5 preferably are arranged to sweep in opposite directions with respect to each other. With this provision, the voltage output of the potentiometer 2 increases as the voltage output of the potentiometer 3 decreases and conversely, as the volt,

age output of the potentiometer 2 decreases the voltage output of the potentiometer 3 increases.

The primary of transformer is centertapped at 53 to provide two sections 8and 9.

One side of potentiometer 2 is connected to one The degree of angular rotation of the two contact arms 4 and 5 is to be taken as being indicative of the positional control which is to be transmitted. The position that is indicated by the dotted line ll indicates a position of null positional control at which the two voltage outputs V2 fr m p tentiomet r 2 and V3 fro pqtentiqw eter 3 are equal to each other. When the arm 4 is positioned to the left of this null position II of the potentiometer 2, a positional control of positive sense will be transmitted and the ratio of V2 to V3 is greater than unity. When the arm 4 is positioned to the right of the null position II on the potentiometer 2, a positional control of negative sense Will be transmitted and the ratio of V2 to V3 is less than unity.

The output signal from the secondary coil I3 is the output signal from the control input device I and is applied to a radio transmitter I2 as modulation to a carrier. The modulated carrier is transmitted from an antenna I3 part of the transmitter I2. In the course of the subsequent transmission of signal, the ratio of the two components of frequencies f2 and is is maintained equal to that between the respective outputs of the potentiometers 2 and 3, namely the'ratio between V2 and V3, or

The signal carrier that is emitted from the transmitter antenna I3 is intercepted by an antenna. I4 of a receiver I5 and is fed as output therefrom to control output device I6.

The intercepted. signal carrier comprises the signal frequencies f2, fa, in the cited example and iszd'emodulatedin the receiver I5. The output of the receiver I5 is fed in common to a desired plurality of filters I8, I9 in the control output device: I6. In the control output device I6, the filter I81 isolates the signal of the frequency f2, and? the filter I9 isolates the signal of the frequency is. from the modulated signal carrier output from the receiver I5.

Thesignal of frequency f2 that is passed by the: filter I8 is: detected by a diode 25 and the rectified. signal appears across a load resistor 42, connected to plate 62 of diode 25, as a direct voltage. whose magnitude is proportional to the amplitude of the alternating signal of the frequency is. The load resistor 42 is in series with the grid utor a direct voltage amplifier tube 22. Signal across the load resistor 42 is of a polarity that. drives the grid 43 of the triode 22 positive. A source of negative bias, that is supplied from a-contactarm 38 on a potentiometer resistor 35, is' in: series with the load resistor 42.

The plate current of the direct voltage amplifier tube: 22 increases and decreases with the overall voltage on the grid 4i} and within a certain range the variation can be made substantially linear. If it be assumed that the negative biasthat is supplied at the contact arm 38 is within a predetermined range and fixed, then the variation of the plate current of the amplifi'er tube 2 2 is proportional to the variation of signal on the grid 40 andso in turn to the variation of amplitude of the component signal of the frequency f2 in the modulation that is carried by the signal that is received by the antenna l4.

In a similar manner the component of the frequency Is in the output of the receiver I5 is isolated by the filter I9= in the control output device It and is detected by the diode 2|. The rectifiedoutput appears across a load resistor 4|,

connected to plate 63 of diode 2|, load resistor 4-I being inseries with the grid 39 of a direct voltageamplifier tube 23 and with a source of negative bias that is supplied froma contact armz3I on apotentiometer resistor 35. The circuiti and operation of the tubes 2| and 23 areanalogous to the circuit and operation that have been described previously for the diode rectifier 23 and the direct voltage amplifier tube 22. Variations in the plate current of the amplifier tube 22 is made proportional to the variation of amplitude of the component signal of the frequency f2 in the modulation that is carried by the signal rat is received by the antenna I4.

The plate current of the amplifier tube 22 passes thru a winding 24 connected to plate 64 of amplifier tube 22 and the plate current of the amplifier tube 23 passes thru a winding connected to plate 65 of amplifier tube 23. The windings 24 and 25 comprise the split field winding of a direct current generator 28 having a rotor 21. The windings 24 and 25 are in opposition with respect to each other so that two electrical currents flowing simultaneously therein tend to set up opposing fields. When the two opposed currents in the: windings 24 and 25 are equal to each other, their fields neutralize each other, and when the currents are unequal, the net field is in the direction that is determined by the stronger current. The rotor 21 of the direct current generator 26 is driven by a constant speed motor 28. The output current from the generator 26 is supplied to the rotor 33 of a direct current motor 29 having a field winding 3|. A constant field is maintained in the field winding 3| of the motor 29 by a battery 32. The direction of rotation of the rotor 30 of the motor 29 is controlled by the difference between the two currents in the windings 24 and 25. The shaft 33 of the motor 29, by its rotation, exerts the positional control which the present invention is designed to effect.

A circuit including potentiometers 35, 3B, and battery 34 is provided to arrest the rotation of the motor when the desired position is reached and.

in the absence of any signal, to return and main tain the positional control in a neutral position. The positive terminal of battery 34 is connected thru lead 66 to the cathodes 44 and 43 of tubes 22 and 23 respectively. Shunted across the battery 34 are two potentiometers 35 and 36 which are connected so that upon movement of contact arms 38 and 31 in the same direction, the voltages tapped off with respect to the cathodes 44 and 43 vary inversely. Contact arm 38 is connected thru lead 60 and resistor 42 to the grid of tube '22, and contact arm 31 is connected thru lead 6| and resistor 4| to the grid of tube 2'3. Since the bias voltages are negative with respect to the cathode, no current will flow between the cathodes and grids. Consequently, the grid bias on each tube will be the sum of the bias voltage and the rectified voltage. The potentiometer contact arms 38 and 31 are mechanically connected to the rotor 36 of motor 29 by a means 33 which is shown as a shaft but may be any suitable coupling means.

In the absence of any positional control signal in the filters I8 and I9, the shaft 33 of the motor 29 will assume'a definite null position, with equal biases on the grids 39 and 40 of the tubes 23 and 22, supplied from the potentiometers 35 and 36, respectively.

A positional control signal that is intercepted by the receiver antenna I4 and is fed thru the receiver I5 to the control output device It when its system is in balance, may be assumed to comprise a strong signal of the frequency f2 that passes thru the filter I8 and a weaker signal of the frequency f3 that passes thru the filter I9.

The strong signal of frequency f2 passes from the filter 18 to the detector to which the filter I8 is transformer coupled as shown, and the weaker signal of frequency f3 passes from the filter [9 to the detector 2l to which the filter I9 is transformer coupled, as shown. The detector 20 will pass a stronger signal to the grid 49 of the tube 22 than the detector 2| will pass to the grid 39 of the tube 23, and, as a result plate current from the tube 22 and passing thru the winding 24 will be in excess of the plate current thru the winding 25 from the plate of the tube 23 and the turning of the rotor 2"! of the direct current generator 26 in the resulting field will create. a voltage and current fiow in the circuit of the motor armature 30.

The turning of the rotor 21 of the generator 26 generates a voltage that causes the turning of the rotor 30 of the motor 29 and of the shaft 33 of the motor 29, to which'maybe attached a position control device such as a rudder. This new position at which the motor shaft 33 stops is the position at which the potentiometer contact arms 31 and 38 on the potentiometers and 36, respectively, become positioned so as to effect biases on the tubes 22 and 23 whereby the plate currents of the tubes 22 and 23 are equalized.

The motor shaft 33 will remain in this particular position as long as the particular positional control signal of paired voltages that established the shaft position is maintained in the filters I8 and i9 and primarily in the output of the device I.

An analogous operational sequence occurs when a positional control signal of opposite sense to that considered above is intercepted by the receiver antenna 14 and is fed thru the receiver IE to the control output device It. In this situation signal of frequency is in the filter l9 is stronger than signal of frequency f2 in the filter I8 and l the detector or rectifier 21 passes a stronger rectified signal to the grid 39 of the tube 23 than the detector or rectifier 29 passes to the grid 40 of the tube 22. Plate current in the winding 25 is also stronger than the plate current in the winding 24. In this instance the output of the generator 26 is of opposite sign to that obtaining for the signal first discussed.

In further comparison with the signal that was first discussed, the rotor 30 of the motor 29 turns in the opposite direction, and the motor shaft 33 turns to a definite control position that is opposite from the null position that is assumed bythe motor shaft 33 as a result of the interception of the signal that has been previously discussed. The motor shaft 33 is held in its new null position by a process of balancing the plate currents in the tubes 22 and 23, as described.

The components of the present device, operating in the described manner, transmit and apply remotely, a positional control thru the agency of relative intensities of two alternating current signals of different frequencies.

The overall system that is contemplated hereby is adapted for transmitting and applying remotely a positional control by the agency of two or more pairs of alternatin current components wherein all of the individual components are of different frequencies. By the adoption of the necessary equipment as disclosed herein for the use of a desired number of independent current components a desired number of independent remote controls can be used. The component frequencies in the composite control signal preferably are not harmonically related, for minimizing mutual interference therebetween.

The use of a pair of signals that are differentiated by their frequencies to effect each control, preserves the signal intact thru accidental changes such as fading, fluctuations in power supply, and the like, whereby the ratio of the intensities of the two components remains intact. The characteristic of the present system whereby one component increases as the other component decreases provides twice the effectual signal change for a given position change as compared with a system using a single signal. These characteristics of the present system imparts improved positiveness in action and improved freedom from accidental interference.

It is to be understood that the circuits and the components therein that have been disclosed herein have been submitted for the purposes of illustrating and describing a suitably operating embodiment of the present invention and that similarly functioning modifications, changes and substitutions may be made therein without departing from the present invention as defined by the appended claims.

What I claim is:

1. In a control device of the character described, comprising in combination a first detector of a first alternating current signal, a first electronic amplifier tube, a first negative gridbias supply, means applying the output of said first detector in the grid-cathode circuit of said I first electronic tube in series opposition with said first negative grid-bias supply, a second detector of a second alternating current signal, a second electronic amplifier tube, a second negative gridbias supply, means applying the output of said second detector in the grid-cathode circuit of said second electronic tube in series opposition with said second negative grid bias supply, an electric generator having a field coil that is split into a first portion and a second portion, means connecting said generator field coil first portion in the plate circuit of said first electronic amplifier tube, means connecting said generator field coil second portion in the plate circuit of said second electronic amplifier tube whereby the plate currents of said first and second electronic amplifying tubes give rise to magnetic fields in opposition, a motor receiving current from said generator and responsive in sense of rotation to the direction of the field of said field coil, control means activated by said motor, a first potentiometer means supplying negative bias to the grid-cathode circuit of said first electronic amplifier tube, a second potentiometer means supplying negative bias to the grid-cathode circuit of said second electronic tube, and means whereby said motor operates said potentiometers to effect equal overall grid voltages in said electronic amplifier tubes and whereby the motor is stopped in a position responsive to the two alternating current signals.

2. A control system comprising a control input device and a control output device, said control input device including a first source of oscillations having a first frequency, a second source of oscillations having a second frequency, means for simultaneously adjusting the amplitude of the first oscillations in one direction and the amplitude of the second oscillations in the opposite direction, a transmitter, and means for modulating said transmitter with the first and second oscillations; said control output device including a receiver for demodulating the output of said transmitter, a first channelconnected to the :output of said receiver including first filter means for separating the first oscillations, first detector means connected to the output-of said first filter means for rectifying the first oscillations, at first electronic amplifier tube, a first negative gridbias supply, and means applying the output of said first detector in the grid-cathode circuit of said first electronic tube in series opposition with said first negative grid-bias supply, and a second channel connected to the output of said receiver including a second filter means for separating the second oscillations, second detector means connected to the output of said second filter means for rectifying the second oscillations, a second electronic amplifier tube, a second negative gridbias supply, and means applying the output of said second detector in the grid-cathode circuit of said second electronic tube in series opposition with said second negative grid-bias supply, an electric generator having a field coil that i split into a first portion and a second portion, means connecting said generator field coil first portion in the plate circuit of said first electronic amplifier tube, means connecting :said generator field coil second portion in the plate circuit of said second amplifier tube, whereby the plate currents of said first and second electronic amplifying tubes give rise to magnetic fields in opposition, a motor receiving current from said generator and responsive in sense-oi rotation to the direction of the field of said field coil, control means activated by said motor, a first potentiometer means for varying the negative bias supplied to the gridcathode circuit of said first electronic amplifier REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 16,667 Hewlett etal July 5, 1927 1,941,615 Mirick Jan. 2, 19.34 2,039,405 Green et al May 5, 1936 2,203,478 Willis June 4, 1940 2,371,415 Tolson Mar. 13, 19.45 2,382,709 Green et a1 Aug. 14, 1945 2,397,475 .Dinga Apr. 2, 19.46 2,441,568 Finison May .18, .1948 

